Ablation of the interior lining of a body organ is a procedure that involves heating the organ lining to temperatures that destroy the cells of the lining or coagulate tissue proteins for hemostasis. Such a procedure may be performed as a treatment to one of many conditions, such as chronic bleeding of the endometrial layer of the uterus or abnormalities of the mucosal layer of the gallbladder. Existing techniques for effecting ablation include circulation of heated fluid inside the organ (either directly or inside a balloon), laser treatment of the organ lining, and resistive heating using application of RF energy to the tissue to be ablated.
An example of resistive heating using application of RF energy to the tissue is described in U.S. Pat. No. 5,769,880, entitled “Moisture Transport System for Contact Electrocoagulation”, issued to Truckai, et al, on Jun. 23, 1998. A system for transporting moisture away from the ablation site is described therein. A build-up of fluid at the ablation site can decrease impedance at the electrode/tissue interface effecting the depth of tissue destruction and efficiency of the procedure.
In some prior art RF devices, fluid drawn from the tissue creates a path of conductivity through which current traveling through the electrodes will flow. This can prevent the current from traveling into the tissue to be ablated. Moreover, the presence of this current path around the electrodes causes current to be continuously drawn from the electrodes. The current heats the liquid drawn from the tissue and thus turns the ablation process into a passive heating method in which the heated liquid around the electrodes causes thermal ablation to continue well beyond the desired ablation depths.